1. Field of the Invention
This invention relates generally to an apparatus for rotationally casting a portion of a tire, and, more specifically, to an apparatus that has a floating alignment mechanism that allows a portion of a mold to move in the radial direction of the tire, which it at least partially forms, allowing the molding apparatus to omit the use of tie bars.
2. Description of the Related Art
An emerging field in tire development involves the manufacture and use of non-pneumatic or hybrid tires that do not depend solely on gas to support the tire structurally as these tires are not prone to deflation, which can render standard pneumatic tires inoperable. An example of such a tire is disclosed by U.S. Pat. No. 7,201,194, which is commonly owned by the applicant of the present application. The content of this patent is incorporated herein by reference for all purposes in its entirety. In an exemplary embodiment of the '194 patent, the non-pneumatic tire includes an outer annular shear band and as plurality of web spokes that extend transversely across and radially inward from the annular shear band and are anchored in a wheel or hub. In certain embodiments, the annular shear band may further comprise a shear layer, at least a first membrane adhered to the radially inward extent of the shear layer and at least a second membrane adhered to the radially outward extent of the shear layer. In addition to the ability to operate without a required inflation pressure, invention of U.S. Pat. No. 7,201,194 also provides advantages that include a more uniform ground contact pressure throughout the length of the contact area. Hence, this tire mimics the performance of a pneumatic tire.
FIG. 1 shows such a tire that defines a radial direction R. For reference, all the reference numerals in the 100's used herein refer to the tire features while all reference numerals in the 200's used herein refer to a molding apparatus for making such a tire and reference numerals in the 300's used herein refer to a features of a floating mold alignment mechanism according to an embodiment of the present invention. The tire 100 comprises a tread 102 that is attached to the outward extent 104 of the spokes 106, which in turn, are connected to a hub or wheel 108 at their inward extent 110 by means known in the art such as by molding spokes between the hub 108 and the tread 102, which have been prepared for suitable bonding to the polyurethane. An outer annular band 105 is located between the outward extent of the spokes and the tread and an inner annular band 107 is found at the inward extent of the spokes, connecting them together. This inner annular band 107 can be used to attach the tire to a hub or wheel.
For the version of the tire 100 shown, the annular bands 105, 107 and spokes 106 are formed by pouring a polyurethane liquid into a rotational mold where the liquid is spread via centrifugation and then cured or hardened. It can also be seen that the spokes 106 are grouped in pairs and that the individual spokes 106′, 106″ within each pair are consistently spaced from each other and that each pair is spaced consistently from the adjacent pair around the circumference of the tire. The spacing within each pair and the spacing between each adjacent pair do not need to be the same. As described by the Abstract and col. 2, lines 28-41 of the '494 patent, the spokes 106 support the tire 100 in tension near the top of the tire 100 and not in compression. Instead, the spokes 106 at the bottom of the tire near the contact patch, which is where the tread 102 of the tire 100 contacts the road, compress or buckle easily. This helps the tire to simulate the pneumatic support function of a pneumatic tire.
Due to the sensitive and important function that the annular bands 105, 107 serve, i.e. to create the bond between the tread and the hub or wheel, as well as aesthetic concerns, it is desirable that the thickness of the bands remain constant. Looking at FIG. 2, mold cores 238″ found on a bottom mold half 234 are shown that form the spokes and inside surfaces 101 of the annular bands. These mold cores are drafted on the surfaces 237 that form the spokes themselves as mold cores coming from one side of the mold interarticulate with similarly configured mold cores coming from the other half (as better described later) so that the thickness of the spokes can remain constant even if there is draft present. However, these mold cores are undrafted on the surfaces 235 that form the inside surfaces of the annular bands. In the case of the inside surface of the outer annular band 105, the inside surface of the tread is substantially cylindrical, requiring that the inside surface of the outer annular band also be cylindrical to maintain the thickness of the annular band and to avoid aesthetic inconsistencies on the outer annular band from one side of the tire to the other. A similar situation exists for the inside annular band.
The depth of the mold cores is equal to or greater than 150 mm, which is a deeper draw than is typical. This added to the fact there are surfaces lacking draft means that the spokes are proned to stick often when demolding. This can cause distortion of the spokes and annular bands and/or undesirable and non-uniform appearance. Any misalignment of the mold halves in the radial direction further exacerbates this problem. Therefore, this problem could be helped if a high degree of mold alignment were present to make sure that movement of mold halves and their associated mold cores was purely translational as mold opening and demolding occurred. This could be facilitated by the use of traditional tie bars that connect the mold platens and guide their movement. However, the molding press and associated platens are designed to open rotationally, about the vertical and horizontal axes, as well as translate for opening and closing the mold. This wide range of movement in addition to the desire to have free access to the interior of the mold for accessing its components as well as a tire being made therein make the use of such tie bars impractical. In addition, the lack of tie bars means that mold platens and mold halves may be misaligned, which during demolding, can cause distortion of the spokes of the tire.
Consequently, damage to the tine often occurs. Accordingly, it is desirable to find an apparatus that allows such tires to be manufactured using mold cores with surfaces that are undrafted using some sort of alignment mechanism. It would be particularly useful if such an apparatus could be designed without the use of tie bars. Finally, providing means allowing adjustment or movement of a mold half in the radial direction of the tire would be helpful.